Nitride-based films are widely used in semiconductor devices and ultra-large-scale integrated circuits. For example, nitride films have been widely used in semiconductor devices as a diffusion barrier for dopants, as an etch-stop film during etching of fine features and as a final passivation film for encapsulation of fabricated devices, among many other uses. Nitride films can be deposited at low pressure or at atmospheric pressure using a variety of processing systems and process gases. These processing systems can perform, for example, thermal chemical vapor deposition (TCVD), plasma-enhanced chemical vapor deposition (PECVD), or remote-PECVD.
Recent innovations to improve complementary metal oxide semiconductor (CMOS) transistor performance have created an industry need for strained ceramic layers compatible with current ultra-large scale integration (ULSI) integration techniques. In particular, channel carrier mobility for negative metal oxide semiconductor (NMOS) transistors can be increased through introduction of tensile uniaxial or biaxial strain on a channel region of the MOS transistor. Similarly, compressively strained films can be used to realize an enhancement in channel carrier mobility for positive metal oxide semiconductor (PMOS) transistors.
Conventionally, strained films have been formed by post processing of films that are compatible with existing fabrication processes. In the case of strained SiN films, for example, a SiN film is formed to a desired thickness, and then treated with ultra violet light to alter the density in a surface region of the film thereby producing the strain. Alternatively, the deposited SiN film can be treated with oxygen containing gases that replace some N in the film with O, thereby producing strain. The present inventors have recognized several problems with these conventional methods for forming strained films.
First, post processing of the deposited film increases production steps thereby reducing throughput, and may require expensive special purpose tooling. In addition, post processing of the deposited film primarily affects the film surface, which limits control of the strain amount and makes some deep treatment processes unacceptably long. Finally, conventional processes deposit the initial film by a CVD process, which can have unacceptable thickness and conformality control for many small feature manufacturing processes now in practice.